From: Patent Tactics, George Brock-Nannestad
Steven Smolian wrote:
> I recall that there is a small reduction in size to a Xerox copy in each
> generation. Does anyone know what percentage this reduction is?
circular strobes with the same number of bars are inherently identical
irrespective of radial dimension. The Record Collector 40+ years ago had a
strip-shaped strobe that you rolled into a cylinder with the appropriate
number of bars and fixed with a paper clip. You simply rested it on the
label. That also was the same irrespective if you had an undersized copy of
Only if you have a paper strip to the width of a magnetic tape that you
splice into your tape for checking the speed of the tape, then the linear
dimensions of the strip counts.
The only problem with photocopies is the fuzzyness on repeated copying. There
might be a small problem with different magnifications in the two directions,
but at most it would make a cyclic movement of your otherwise stationary
strobe image when you light it with 120 Hz light (such as a fluorescent
light, the older the better). Having the wrong center would be worse: your
impression of the strobe image would be just like it would sound if it were a
> The speeds start at the outside at 107.44 rpm, then 109,08 rpm, and
> successively to 116.13 rpm on the most inner of the 6 sets of dots.
> speed for the wire is 24 ips, at least in one source.
----- these figures do permit some juggling to convert rpm to ips. First you
divide by 60 to obtain revolutions per second. One revolution is one
circumference of the take-up reel, which is PI times the diameter (which you
need to measure, unless it was absolutely standard). Then you know that this
length of wire gets onto the reel per second at the rpm indicated by your
stationary strobe image on the strobe disc.
This was a good capstan-less transport, and they used the large diameter to
ensure that only a few layers of wire came on this reel, so that the diameter
increase (and hence increase in ips) would almost not be audible on the same
piece of wire.
So, in conclusion: the reduction in size in Xerox copiers (to avoid black
margins) is irrelevant (and it was adjustable by the technician anyway).